Скачать или смотреть AEU38: Using Class Modules in the Real World (Anders Ebro)

Anders Ebro, is a former MVP from Denmark, known online as The Smiley Coder and he loves Lego! He is a Danish software architect with a passion for application and software development.

Anders provided an introductory session on class modules – and explained how to use them in real world scenarios.
The session included:
• How do you decide whether to put your code in a bunch of procedures in a standard module, or to create a class module?
• What factors should guide that decision?
• Class modules can raise events, but beyond that, what are the benefits?
• Why use properties, rather than public variables in a standard module?

Anders gave real life examples of when class modules have been used and why he did it that way.

You can now download a zip file which includes the presentation, example app & code in the same ACCDB file from https://www.isladogs.co.uk/aeu-38

TIMES
0:00:00 Colin - welcome to the Access Europe User Group and to this month's presenter Anders Ebro
0:01:04 Anders
0:01:23 Start of presentation - background info
0:02:34 Session overview
0:03:40 Why (many) Access developers rarely use classes
0:04:23 When should we use a class?
0:05:03 What is a class?
0:05:28 A Class(y) example - calendar class
0:06:24 The 'simple' way - no classes / no functions - much repeated code for each date textbox - inefficient and hard to test / maintain. Can reduce repetition using functions
0:08:16 The 'classy' way - class module clsDateDisplay to support displaying all dates in all weeks of month / mouse click / 3 types of highlighting
0:09:55 Object initialization in VBA
0:11:02 DateDimension table
0:12:10 Initialize clsDateDisplay
0:12:52 Event Definition in calendar form
0:13:40 Event Listener in clsDateDisplay - use of WithEvents keyword. Manage appearance of 'out of month days'
0:16:57 Fixed issue with missing / greyed out dates in display - RaiseEvents / added collection to store dates and prevent these going out of scope / fixed year-month definition
0:20:17 Comparison - RaiseEvents vs using calling code to set variables - analogy with different ways of alerting people to a fire - telling/instructing vs listening/reacting
0:22:09 Create Mouse Action Event to show mouse position over date texboxes. Add mouseover to form detail section also
0:27:15 Add custom listener to clsDateDisplay and add highlighting
0:30:27 DEMO of result
0:31:51 Add day of week highlight
0:32:55 Using the calendar form to filter data in other forms
0:36:56 Object cleanup - set to nothing when calendar is unloaded
0:39:29 Inheritance / interface are more advanced class concepts and not covered in this demonstration
0:39:43 Thanks to Anders for an excellent presentation.
0:40:19 Q1: Neil - Did the events in the calendar form need to be Public rather than Private? A1: Yes - even if not called from other forms
0;41:30 Q2: Summary of long discussion re Let & Set code. Use Set for objects and Let for variables
0:42;36 Q3: Colin - there was no YearChange code similar to that for MonthChange. Is the latter automatically invoked on a year change? A3: No.That code is included in final version
0:43:24 Q4: Tim J - asked how the date data was generated in tblMonth. A4; Code used in module z_DateProp
0:43:57 Q5: Domenico - asked about event hierarchy in RaiseEvents code when both calendar and more than one form is involved. Also what if an error occurs in one of these?
A5: good question! Simple test using message boxes appeared to show it was in the order forms were opened. Then re-tested first with unhandled errors & then handled errors.
0:48:33 Q6: How well would this work without a saved dates table & just generating date info 'on the fly'? Has used both approaches. Both work. However if want to include e.g. public holiday / fiscal year info, then table approach helps
Also performance significantly improved in SQL Server using date table.
0:50:23 Q7: Jim F - why necessary to open calendar form first? A7: Using the approach in this demo, the listening object must have a variable declared WithEvents.
0:51:34 Thanks again to Anders for a very clear introduction to the use of class modules
0:52:25 Next month: Karl Donaubauer (MVP) will explain how best to handle issues related to update bugs
0:54:19 Access Devcon - 10/11 April - outline of topics / speakers
0:56:39 Final comments - see you all next month
0:57:08 End